I don't know what the difference is between the Focus and the Edge, but the manual for my Edge says to turn the key all the way back toward off. When the transmission is in the neutral position (for an automatic transmission) the key does not go all the way to lock, so the steering wheel stays unlocked and the wheels track freely to the right and left. You just have to make sure all electronics (stereo, auto light switch, air conditioner fan, etc) are off to prevent battery drain. I have been towing our Edge for over five years and have never had an issue. If you have a manual transmission, the procedure may be different.
RognBon
1997 Monaco Dynasty 40'
Cummins 8.3 325 HP
2008 Ford Edge Toad